If your wall cabinets do not extend all the way to the ceiling, the duct can be run above the cabinets and exit to the right side. If the ceiling in the DR is the same height as the kitchen, and the floor joist direction cooperates, the duct may run through the ceiling over the DR. Some exploratory action is called for.
Casey

"they aren't thrilled" - problem 1 - who is 'they' and why aren't they thrilled? Venting should be a priority in a new/reno kitchen - "they' must be people who don't cook or clean

Are the plans set in stone/cabinets ordered? If this were my kitchen I would have the range moved to the right & install proper venting straight out the exterior wall

That said, if the plans are set - You could go up make a right elbow (which cuts the down on the efficiency cfms of unit) - that would take some exploring to determine the ducting can go that path - If the kitchen walls are open now - you shouldn't have a problem figuring

Don't bother with downdraft - just do a search here or over on kitchen forum - 1st thing people who do renovate is rip our the ineffective/worthless downdraft

good luck - & I would have a serious conversation with the person/people responsible for your kitchen design - why wasn't this part of the design from the start?

Venting our range hood was about the most challenging part of our remodel. Our range is on an interior wall that is adjacent to our formal dining room, too. An additional issue for us is that just outside the dining room is a screen porch.

Our floor joists did run the "right" way - revealed the minute we took out the old cabinets. But our first idea, going directly out to the right, landed the vent in the soffit of the porch. So we had to do 2 right angles and come out above the window (which is roughly where your doors are). Total run is probably 12 feet so when we did the calculations based on our range hood (Zephyr Venezia), we were fine in terms of CFMs.

Our cabinet maker and the sheet metal guy had a heated argument about how to run the venting (sheet metal guy was lazy, cabinet guy knew it could be done but would be challenging).

In the end we used rectangular ducting and ran it in the space between the floor joists in the first run, then a slight dip and up against the floor joists to the exit to the outside. Our upper cabinets go to the ceiling and include about 4" of crown molding, so I actually didn't lose any cabinet space. Is that an option for you?

The rectangular ducting (10 1/4 wide x 3 3/4 high x 6 long, I think) provided the same exhaust capabilities as the 6" or 7" round we had originally thought we would use, and allowed us to "hide" it above the cabinet, in the space between the cabinet box and the ceiling that is now beautifully covered by crown molding.

I don't have pictures with me, but I could probably post some later tonight if you wanted to see how we did it. I think you can also email me from my page.

Thank you all for your responses. I couldn't agree more that venting should be a priority. We are still in planning stages so nothing is set in stone yet.

Sailinggal, your experience has been so helpful.

The one cabinet guy who I am leaning most toward going with (he's custom) is the one who is giving me the least flack about this. He is the only one who even puts any merit in venting to the outside. However, he did believe that you could not use the rectangular vent for the entire run. He said you'd have to convert to round at some point. So that is good to know that you used rectangular the whole way and it works! Rectangular would be so much easier! And yours sounds a little more complicated than mine would be, and it still works, so that gives me hope!

If we went through the cabinets, that would maybe be an option. I ran that idea by the custom guy this morning and he said it would be a last case resort, but likely do-able if we absolutely had to. It's complicated by the fact that it would have to run through a to-the-ceiling hutch with glass mullion doors.

I would love to see pics of what you did. We could use any help we could and would maybe even be able to use yours as a model. That would help us maybe in even knowing what we need to tear up in terms of sheetrock to explore what's inside. I will try to find your email on your page.

Regarding the shape and size of the ducting, I would check with the manufacturer of the hood and the building code for your jurisdiction. The last thing you want is to do the duct work and then find out it was not done to code and have to rip it out.

It there a reason the range can't be moved down to the right? If there is then I would consider over the range go up as high as you can, turn to the right as you face range and go directly out the wall.

I agree with a previous poster that going above your cabinet, then turning to the right until you reach the exterior wall, and then vent to the outdoors. The height of your ceiling is obviously a consideration, as is the height of the cabinets you are planning. Ideally, if you have a soffit above the cabinets to the right of the range, the ductwork can be hidden in the soffit. An alternative would be to position the range to the right of its present planned position, so that it will be against the exterior wall. That will simplify the installation.

Other considerations: needed cfm capacity, distance between range top and hood, minimizing noise level, etc. These are covered in detail in previous threads in the KITCHEN forum. Do a search there and you'll learn more than you ever wanted to know about kitchen exhaust systems. It is a complicated and frustrating thing, but you're lucky that you're planning it now. For many people it's an afterthought, when it's almost too late to do it right.

Even if you don't have a soffit to run the thing through, you might not mind having the duct in the cabinets. I know I wouldn't, being sort of short and not absolutely enamored of high back-of-the-cabinet storage.

If you move the range over to the right to give easy venting, you'll have to move the table and redo the entire layout.

Ducting can be rectangular over its entire length, except where it has to transition to some other sectional shape at one end or the other. Rectangular duct of the same area as circular duct has more friction (pressure loss), but using transitions just to get to circular may induce enough flow disturbance that there is no net advantage in doing so. And in some configurations, a larger area rectangular duct can be fitted than circular.

Duct size should strive to keep the air velocity under full fan flow in the 1000 to 2000 feet per minute range. This minimizes depositing the greasy effluent particles that are too small for the hood to collect in the duct. In other words, if a modest ventilation fan is used, don't go for overkill in duct size.

kas

I am having the same problem---I posted a photo of my problem on another entry in the kitchen forum. Thank you for posting the photos, SailingGal!!

Thanks for the post..this has been helpful!

I hope this is a simple question: I have an existing range-hood mounted under a bank of cabinets over an island. So you see both sides of the range hood. The ducting runs straight up, through the cabinets, through the roof. I am replacing the cabinets and range hood. I want to use a slim island-mount range hood. I notice that there are vents in the vertical housings of island-mount range hoods. What purpose they serve, and does that prevent the ducting from doing through the cabinets?

VBM: I don't specifically know the answer to these two questions, except that there are a few hoods that use filter packs and recirculate air back into the room through vents in the housing. There are no duct vents in my Wolf Pro Island hood that exhausts outside.

Hood configurations that are slim in height may have difficulty properly capturing and containing the rising cooking plumes, relative to conventional pyramidal hoods. Perhaps you could specify a candidate hood and your goals for hood performance and further comment could be made.

Thanks for your help. Here's a link to one I am looking at.

http://www.kitchensource.com/range-hoods/cav-sv218z2-i.htm

If you go to "view 2" you see the grid on the vertical housing. That would make no sense at all for through-roof venting. But you make a good point, that the housing could be designed for either vented or filtered applications (this unit can be configured either way). So perhaps that grid is for that application.

As for performance, this would be over a glass cooktop. I picked this for it's slim profile, but I certainly don't want the cooking steam to end up all over the cabinets. Are you of the opinion that I should consider one of the curved-glass alternatives?

Thanks again for your help.

Valerie

Here's a link on Houzz

https://www.houzz.com/products/cavaliere-euro-36-island-mounted-range-hood-prvw-vr~55462589

The curved glass styles are even less effective at capture, judging from their appearance. The issue in both cases is lack of sides to provide a capture volume that overlaps the rising and expanding grease and moisture effluent. However, if the air flow is adequate, effluent rising to the mesh or baffle filters should generally be pulled through and contained. Any effluent that does not impinge on a filter will likely reflect off of the hood (or miss the hood) and dissipate into the room. Assume that the cooking plume expands from any hot pan base at an angle away from the vertical of roughly 10 degrees. You may be able to evaluate for a given hood filter size what portion of the plume is not contained by the hood for each burner.

The duct cover slots look to me like they are intended to work with the recirculation option. Without this option, these shouldn't be emitting any air, so their presence shouldn't cause a functional penalty. If there is an aesthetic penalty, some other brand may be similar without the slots.

Which size unit were you intending to use?

Do not assume that a mesh filter hood (even with clean meshes) and a six-inch duct to the exterior will actually move the rated flow rate of 900 CFM. Although actual flow will depend on many factors, including the pressure losses in the make-up air path, the mesh area, and the unspecified fan curve shape, you should de-rate declared zero static pressure blower flow rates to 2/3 or less. That may still be adequate.

Reviewing various hood threads on this forum may provide additional insights.

kas

I think your question has been addressed, but I wanted to point out that a 6 inch duct is going to be louder than a larger one. The larger the duct, the mmore room for the air to move, so you have less resistance and therefore, less noise. I felt 8 inches was minimal.

If your current duct goes up through the roof and you are not relocating the cooktop or vent, there shouldn't be any reason the new one can't do the same. Perhaps your guys just don't want to get on the roof. Even if the exterior vent isn't changed, the roof needds to be checked after things have been moved and reconnected to make sure nothing has lifted and left leaks. A roofer can do that if your cabinet and appliance guys are not comfortable with it.

Thanks very much to both of you. I see that many vents have a 6"/8"/10" option, so I may look for one that has that option, because my existing is wider than 6". I appreciate the generous sharing of your experience. I think I have what I need to make a wise decision.

We have a Zephyr Verona island vent hood with the same grid cutouts near the top of one side. I saw the hood when they installed it and I don't think the grid has anything to do with actual venting. However, there is a substantial fan motor inside the housing, and I think that grid just provides some cooling air for the fan motor.

If your inspector follows the new code rules, any fan that flows more than a certain CFM will require a make-up air vent. Our Zephy hood could be jumpered so that its fan speed/flow would be limited and it would not require make-up air. However, the local inspector never even brought the subject up, so ours is jumpered to allow full flow.

Bruce